Perception of salty tastes by humans is influenced by gender, but this phenomenon has been largely unexamined in animal models, even in species such as rat in which much is known about the peripheral mechanisms and central pathways involved in the processing of taste information. Most studies have examined the ingestion of NaCI solutions rather than the taste. Sex differences have been reported in NaCI ingestion stimulated by experimental methods to produce a sodium deficit. Similarly, sex differences in spontaneous, need-free intake of and preference for NaCI by rats during long-term tests also have been reported. In both cases, removal of estrogen by ovariectomy eliminated sex differences in NaCI intake. However, estrogen also has substantial effects on body sodium and fluid regulation. Thus, given the post-ingestive consequences that occur during prolonged ingestion, and the use of experimental methods that disrupt body sodium and fluid balance, these results may provide limited information about sex differences in NaCI taste responses. A few studies using taste reactivity procedures to more directly examine taste responses indicate that there are sex differences in the responses to NaCI taste in rats, but the role of estrogen was not specifically evaluated. Moreover, the basis of sex differences in taste responses to NaCI remains virtually unknown. Within the central nervous system, responses of neurons in the parabrachial nucleus to sapid NaCI are affected by estrogen. Thus, sex differences in behavioral taste responses to NaCI may be attributable to direct effects of estrogen on central gustatory pathways. Alternatively, differences in peripheral sensory neural responses to NaCI may contribute to sex differences in taste responses by altering the sensory information that ultimately stimulates activity in central gustatory pathways. At present, little is known about the effect of estrogen on peripheral sensory responses to NaCI taste or on activity in central gustatory pathways in rats, or about how such effects may contribute to differences in behavior. This application will use behavioral, electrophysiological, neuroanatomical, and immunocytochemical methods to address these questions, thereby providing better understanding of the influence of estrogen on gustation. Ultimately, such information may be useful in understanding sex differences in other behaviors.